Merc Thunderbolt IV ignition coil...internal resistor or external such as resistive wire? I know there is no external resistor as such.

If you're asking if you need a resistor, no.
If you need a coil, an $8 automotive (external resistor) works fine with full 12V on the T bolt IV.
A lot cheaper than the $40 Merc coil.

I was thinking about replacing mine with hotter ones. Just wondering what I need...internal or external

I had an external resistor on my ignition two boats ago. The purpose was to lower the current to the points during idle so points would not get burned. From my experience, having the resistor on electronic ignition causes no harm, so I think you can use what ever you like. I am running the blaster II MSD with the tbolt 4.

BT

But B.T. , do you have a resistor on the MSD Blaster coil??? Because by adding a resistor to a coil that has an internal resistor you can hurt your performance and really make it hard to start.

TIA

I don't think the blaster 2 has a resistor internal. I have not added external either, don't know what purpose it would serve since I don't run points. Maybe I am missing something. I run the 6al ignition amplifier controlled by the tbolt ignition with blaster 2 coil making the fire. Starts great with or without the 6al. I do believe the merc coils I removed had a label that said the coil could be used with an external resistor, but I never paid much mind to that, again thinking it is for points.

Please enlighten me if I am in the dark... would love to find out I am doing something stupid and by changing a wire get 5 more mph

BT

My MSD book says you may wire in a ballast resistor if problems with engine runon are experienced. They say it eliminates voltage leakage after the key is shut off. That is all it says.

BT

BT,
I got an answer elsewhere stating there is resistive wire in the Merc harnas and you don't need to add one externally
Thanx

The Tbolt IV will have a purple wire going to the coil. No resistance wire. I have seen older harnesses with Tbolt setups and resistance wires. These are easy to ID since they'll have a yellow bypass wire from the starter to the + post on the coil and the resistance wire is silver.
They seem to work fine either way.
I would get an external resistor coil, skip the ballast resistor/wire and wire 12V directly to the coil. I've been running auto coils on T bolts like that for years.
Gary